Garden & Lawn Testing Interpretation

Now that you have had your lawn or garden tested it is important to understand what the results mean. Our garden/lawn report is divided into 3 sections. First, the lab results for each analyte, second, the interpretation of that test (i.e. sufficient or deficient) and lastly a recommended fertilizer addition.

Test Results

pH and Salts

pH and Salts are measured on a 1:1 slurry (1 part soil, 1 part water). pH is the measure of acidity or alkalinity in the soil. The pH scale is from 0-14, with 7 being neutral. Soils with a low pH (less than 7.0) are considered acidic, while soils with a pH greater than 7.0 are alkaline. To lower soil pH elemental sulfur can be added. To raise soil pH lime products can be added. Ideal soil pH is plant specific, however, near or slightly below neutral soil pH will work for most plants. Soluble salts are present in all soils. If salt levels are too high (generally greater than 3 mmhos/cm), then plant injury can occur. The reason plants struggle in high salt conditions is because the concentration of salts in the soil is greater than in the plant. This means that the soil can actually pull water out of the plant. The common response is that the plant will look dry even when the soil moisture is adequate! The best way to remediate this is to apply clean water in excess of the plant needs and allow the salts to leach beyond the root zone.

Organic Matter

Organic matter is the measure of the non-mineral portion of your soil and is considered beneficial. Organic matter improves several soil physical properties (soil structure, water holding capacity, permeability, etc.) and chemical properties (nutrient holding capacity, release of nutrients). Compost, manure, and other sources of organic materials can increase organic matter. These sources can be high in salts, so be prudent in applying them.

Nitrogen

Plant available nitrogen exists in two primary forms: nitrate (NO3-) and ammonium (NH4+). The combination of these two, in addition to a contribution from the soil organic matter, indicate how much nitrogen is plant available. Nitrogen is responsible for several functions in the plant including amino acid production, shoot growth and fruit set.

Phosphorus

Phosphorus extraction methods vary by region. If the soils in your area are generally low in pH we use a weak Bray (P1) extraction. For soils in a high pH region we use Olsen. Phosphorus is very important for energy production in the plant.

Potassium

Potassium, like nitrogen and phosphorus, is a macronutrient. This means that compared to other plant nutrients they are required in larger amounts. Potassium is vital for several plant functions including: nutrient uptake, transpiration and enzyme activity.

Interpretation

Graphical representations are given for the different parameters. For pH the scale shows where in the range of acidic-neutral-basic your soil falls. For salts the interpretation is given as low-medium-high with any value >3.0 mmhos/cm being high. No interpretation of organic matter is given because plants can grow well in both low and high soil organic matter conditions. Generally, wetter climates tend to have soils with more organic matter. All other tests are interpreted as Deficient-Sufficient-High. Deficiency and sufficiency are unique to each test and are based on available data from Universities for both lawns and gardens.

Fertility Recommendations

Fertility recommendations for Nitrogen, Phosphorus and Potassium are given here in pounds per 1,000 square foot. If you get a fertilizer recommendation for nitrogen, phosphorus or potassium you will notice that the nutrients are expressed as N, P2O5, and K2O. This is important because when you purchase a bag of fertilizer the numbers on the bag are expressed as N, P2O5, and K2O. These numbers are the percent analysis for those nutrients. For example a fertilizer bag with an analysis of 16-16-16 means that 16% of the weight of the product is N, 16% is P2O5, and 16% is K2O. This means that if you have a 100 pound bag of 16-16-16, it contains 16 pounds of N, 16 pounds of P2O5 and 16 pounds of K2O.

To accurately calculate how much product to apply use the values in your soil test recommendation and divide by the analysis value. For example, if your test says to apply 7 lbs of N per 1,000 ft2 and you have a bag of 46-0-0 the math is as follows: [7 lbs /(46/100)] = 15.2 lbs of 46-0-0 per 1,000 ft2.

If you wish to apply an organic amendment you will need to know the analysis of that material. If you are able to get that information, then the math is used in the same manner.